Ultrasound Scanning of Neonatal Hips

Transcription

1 Ultrasound Scanning of Neonatal Hips Dr. Dickson S F Tsang Associate Consultant Queen Mary Hospital Why? How? What? Outline IAAHS 2nd April, 2011 Outline Why? Why performing hip ultrasound (USG)? Why USG? How? What? Outline Why? How? How to perform? How to interpret? How to perform better? What? Outline Why? How? What? What does it look like? What is your question (Q & A session)? The Paediatric Hip Femoral head - non-ossified at birth Ossification takes place 2-8 months Ossific nucleus is not anatomically the centre of the femoral head USG becomes increasingly difficult with age Practical up to 6 months of age 1

2 Paediatric Hip USG Aim = to diagnose DDH < 3 months >3 months = late diagnosis: potential risk of irreversible hip dysplasia / early OA Sensitivity & specificity near 100% False +ve and ve: ~1% and 2% <30 d/o: physiological laxity of hip 1st scan at 4-6 weeks of age Paediatric Hip USG Developmental Dysplasia of Hip (DDH) A spectrum of abnormalities Commonest MSK disorder in children (Incidence : 1000 births) 9-10% of all hip replacements Female >> Male (4-8 : 1) Left > Right (3 : 1) Can be asymptomatic in the early phase Hip development, maturation, stability & degeneration Why performing hip USG? Early detection (age related) Growth potential Ossification potential The later the diagnosis is made, the harder the treatment will be, leading to greater risk of complications and a higher chance of failure Avoid damage No treatment (deformity) Over treatment (Avascular necrosis) Why using USG? USG vs Clinical exam USG Diagnosis of DDH Monitor treatment Why using USG? Not need to sedate the patient High resolution Multiplanar Dynamic Radiation-free Objective & Subjective Why using USG? USG vs Clinical exam USG vs XR vs CT vs MRI 2

3 Clinical Exam USG XR CT MRI High resolution Osseous parts Multiplanar Dynamic How to perform & interpret? Radiation Free Objective/ Subjective Objective Objective / Subjective Objective Objective Objective Y cartilage The Y-shaped connecting cartilage in the acetabulum that joins the ilium, ischium, and pubis Lower limb of os ilium centre of the acetabulum in USG Gray s Acetabulum Perichondrium Acetabular labrum Osseous rim Acetabulum Bony portion Cartilaginous portion Hyaline cartilage of the acetabular roof A few echoes only and looks like an echo gap Fibrocartilaginous acetabular labrum Triangular in cross-section Highly echogenic 3

4 1. Labrum 2. Lower limb of os ilium 3. Cartilaginous part of acetabular roof Perichondrium Lateral boundary of the cartilaginous acetabular roof Distally continuous with joint capsule (less / no echo) [perichondrial gap] Proximally merges in to the periosteum of the iliac bone (thick) [proximal perichondrium] May mistaken as the acetabular labrum 1. Proximal perichondrium 2. Perichondrial gap 3. Acetabular labrum Acetabular labrum Triangular in cross-section On inner side of the joint capsule, but not connected with it Fixed to the hyaline cartilage acetabular roof Tips for identifying the labrum (4 guides) Acetabular labrum Tips for identifying the labrum (4 guides) 1. The labrum echo is always lateral and distal to the echo gap of the hyaline cartilage acetabular roof on the inner side of the joint capsule 2. The labrum is always in contact with the femoral head 3. The labrum is always caudal to the perichondrial gap 4. The labrum is where the contour of the joint capsule diverges from the surface of the femoral head Labrum definitions Lateral and distal to the echo gap of the hyaline cartilage In contact with femoral head Caudal to the perichondrial gap Joint capsule diverges from the surface femoral head 4

5 Labrum definitions Lateral and distal to the echo gap of the hyaline cartilage In contact with femoral head Caudal to the perichondrial gap Joint capsule diverges from the surface femoral head Osseous rim Most lateral point of the concavity of the bony socket The point where the concavity of the bony acetabular roof changes to the convexity of the ilium (where the concavity becomes the convexity) What to look for? 3 major components of DDH: Bony rim definition 1. Concavity (bony acetabular roof) 2. Turning point (measurement point) 3. Convexity (of ilium) 1) Morphology 2) Position 3) Stability How to look for? The 3 views 5-7 MHz, linear probe Three distinct methods: 1) Static method by Graf (morphology/position) 2) Femoral head coverage by Morin (Terjesen) method (morphology/position) 3) Dynamic method by Harcke (stability) 1) Coronal view in Graf format 2) Transverse view with hip flexion 3) #2 with Barlow s stress maneuvre 5

6 Coronal view Angle adjusted max. depth of acetabulum Hip either in neutral / flexed position Neutral position usu o of hip flexion Flexed position 90 o of hip flexion Independent of hip / leg position Femoral head coverage Problem(s) Oblique angle made to look erroneously deep or shallow Precise plane of imaging is a critical issue demands training and audit of the technique What to look for? 3 major components of DDH: 1) Morphology Morin (Terjesen) method Graf technique 2) Position Morin (Terjesen) method Graf technique 3) Stability Morin (Terjesen) method Femoral head coverage Coverage of the femoral head by the bony acetabulum in the standard coronal plane Acetabular development Distance between medial aspect of femoral head and the baseline (d) Maximum diameter of the femoral head (D) d/d x 100% Technique 6

7 Technique Technique Popular in central Europe A single coronal image of the hip irrespective of position of femur Lateral position Hip flexed to 90 degrees Must have presence of 3 structures on the same plane: 1) Lower limb of bony ilium (must be parallel to the probe) 2) Middle of bony acetabular roof 3) Cartilaginous acetabular labrum Measurement Technique (Graf) Baseline Roof line (bony roof line) Inclination line (cartilage roof line) α angle (bony part) β angle (cartilaginous part) Measurement Technique (Graf) α angle & β angle Independent of the position of the baby position of the femoral head position of the leg femoral head ossification 3 lines Baseline Roofline Inclination line 3 lines Baseline A line drawn through the plane of the ilium, where it connects to the osseous acetabular convexity Roofline Inclination line 7

8 Baseline A line drawn through the plane of the ilium, where it connects to the osseous acetabular convexity 3 lines Baseline Roofline A line drawn through the plane of the bony acetabular convexity Inclination line Roof line (bony roof line) A line drawn through the plane of the bony acetabular convexity 3 lines Baseline Roofline Inclination line A line drawn from the osseous rim to the middle of the labrum Parallel to the cartilaginous roof Inclination line (cartilage roof line) A line drawn from the osseous rim to the middle of the labrum Alpha angle (α angle) A measurement of acetabular concavity The angle between baseline and roofline 8

9 α angle Alpha angle (α angle) A measurement of acetabular concavity The angle between baseline and roofline Normal > 60 o o may be physiologically typical in neonate (<2-week old) < 50 o considered abnormal Beta angle (β angle) A measurement of the acetabular cartilaginous roof coverage The angle between baseline and inclination line β angle Beta angle (β angle) A measurement of the acetabular cartilaginous roof coverage The angle between baseline and inclination line Normal < 55 o The smaller the angle, the less the cartilaginous coverage and the better the bony acetabular coverage of the femoral head Sonographic hip type Correlates with the pathological changes in the hip joint (cartilage & bony socket) rather than with the height of the dislocated femoral head The more accurate and precise the typing, the more appropriate and precise the treatment can be 9

10 Sonographic hip type 4 main sonographic types Bony roof (α angle) Superior bony rim Cartilaginous roof (β angle) Age (subtypes) Type III and IV are both decentered hips with different deformations of the hyaline cartilage roof NORMAL FOLLOW UP TREATMENT Myths Truth The 3 lines should intersect at 1 point!! The 3 lines seldom intersect at 1 point Only type 1 joint with sharp bony rim has 3 lines intersect at 1 point ( ~20% of all type I joint ) 10

11 3 Landmarks 1. Osseous rim 2. Ilium 3. Acetabular labrum Effect of tilting 1) Anterior sectional plane 2) Standard plane 3) Posterior sectional plane A hip USG can only be evaluated if all 3 landmarks are shown Effect of tilting Only mid (standard) sectional plane should be used for measurement The tilting can be distinguished from the shape of iliac bone proximal to the bony acetabular rim Problems technique requires supervised training with considerable learning curve Studies have shown poor reproducibility for placement of lines Interobserver & Intraobserver error Problems Latest literature cast doubt on diagnostic validity and reliability of USG hip in infants Great uncertainty in the group with alpha angle <60 and >43 ( II) Significance of II unknown No true information on prognosis No universal agreement on management decision (US vs clinical) What to look for? 3 major components of DDH: 1) Morphology 2) Position 3) Stability Harcke dynamic method 11

12 Dynamic Technique Harcke dynamic method Relaxed hips x for instability Supine or lateral decubitus position Transverse images of hip (posterolaterally) Stress image in transverse plane Hip flexion, adduction with gentle posterior push >/= 2mm displacement Hip Abduction Hip Adduction Dynamic Hip Assessment Objective Position of the femoral head Normal Subluxated Dislocated Stability of the hip (motion & stress) Normal Lax Dislocatable (Reducible / Not reducible) Dynamic Hip Assessment Transverse flexion view (Harcke) Flexing the femur 90 o Transducer maintained at posterolateral position over the hip joint Metaphysis Femoral head Bony acetabulum Sonogram changes its appearance in abduction and adduction (U V) 12

13 Dynamic Hip Assessment Stress (gentle posterior push + adduction) Barlow test Dislocation Posterior + Lateral displacement +/- Superiorly displaced Disruption of normal U pattern Reduction Abduction Ortolani maneuver US Report 1) Appearance of bony and cartilaginous acetabulum, alpha + beta angle 2) Appearance of femoral head 3) Position of femoral head in relation to acetabulum at rest 4) Dynamic stress view findings Points for sharing How to perform better? Clear instructions to mother / accompanying person Mother / accompanying person at opposite side of the table / bed Calm and stablize the baby by putting her / his hand on the baby s shoulder Screen the L hip first Points for sharing Legs need not be straight during coronal view Do not flex your fingers Fingernails could scratch the baby and cause struggling Avoid tilting the transducer May cause error in measurement Points for sharing The plate of iliac bone (NOT spine) must be parallel to the surface of probe Gentle force for stress image Use pedal to help Messy! Practise more!! 13

14 Who to screen? Evidence is lacking either for or against a generalized screening of all child for DDH Conclusion: routine use of USG hip in all neonates cannot be recommended Screening for those with risk factors: 1. Breech presentation 2. Family history 3. Club foot / torticollis Summary Hip USG enables accurate analysis of the patho-anatomical situation in the hip joint Early detection becomes possible, so that the hip joint has lots of time available when there is good potential for maturation 4. Positive physical examination Summary Coronal + Transverse scans Redundant To confirms findings the level of confidence Widespread availability of USG A/v in many areas USG hip Diagnosis Monitor treatment Summary Over-aggressive treatment Damage the growing epiphysis deformity & delay in ossification Avascular necrosis of femoral head Cost impact on health care system Cost of screening VS treatment Problems? How and when to treat? Universal screening? Splint treatment in all abnormal cases Better ultrasound today than a limp tomorrow! 14

15 Reference Developmental dysplasia of the hip -- Child; ACR Appropriateness Criteria; Hip ultrasonography in infants and children; A. Karnik; Indian L Radiol Imaging; 2007; 17: Ultrasonography in the diagnosis and management of developmental hip dysplasia (UK Hip Trial): clinical and economic results of a multicentre randomised controlled trial; D. Elbourne, etat.; The Lancet; Vol. 360; Dec 21/28, Paediatric Musculoskeletal Disease with an emphasis on ultrasound; A.L. Baert, K.Sartor, Springer. Hip Sonography, Diagnosis and mangement of infant hip dysplasia, 2nd edition; R Graf, Springer. Thank you!! 15